Not applicable.
Tetraalkyl ammonium halide salts can be used as phase transfer catalysts. An example of such a compound is ALIQUAT(copyright) 336 quaternary ammonium compound, a methyl tri-alkylammonium chloride, wherein the alkyl groups are a mixture of C8 and C10 groups. Phase transfer catalysts (PTC) convey anions into an organic reaction phase at a higher concentration and activity than would be the case without the PTC. In functioning as a PTC, the chloride must exchange for the desired anion, which is not always a favored equilibrium. If the anion on the PTC reagent is other than chloride such as phosphate or bisulfate, it will more readily exchange for other anions, resulting in a more efficient catalytic effect. In addition, other quaternary ammonium salts such as hydroxide, carbonate, nitrate, chromate, dichromate, vanadate and tungstate are useful for other applications such as in hydrometallurgical extraction processes or as reagents in chemical processes, but are difficult to prepare by normal methods.
There are several known methods for converting quaternary ammonium chlorides such as ALIQUAT(copyright) 336, a methyl trialkylammonium chloride, to quaternary ammonium salts having anions other than chloride but each has its disadvantages. For example, to convert a quaternary ammonium chloride to a quaternary ammonium bisulfate, an organic solution of a quaternary ammonium chloride salt can be contacted with a sequence of aqueous solutions of sodium bisulfate or sulfuric acid, but because the equilibrium is unfavorable, a large excess of the aqueous solution is required in an extended series of contacts to reach a low level of chloride. The chloride salt can also be reacted with dimethyl sulfate to produce methyl chloride and the methylsulfate quaternary ammonium salt, which is subsequently hydrolyzed to the bisulfate and methanol, but this is expensive and involves highly carcinogenic materials. The chloride salt, usually in a diluent to reduce viscosity, can be heated with solid sodium bisulfate, to precipitate the less-soluble sodium chloride, but this requires repetitive equilibrations with excess sodium bisulfate and difficult filtrations. At least four repetitions are needed to reduce the chloride level by 90%. In addition, this method tends to produce significant concentrations of free sulfuric acid in the quaternary ammonium phase. A method that would allow rapid conversion of the chloride to another anion such as the dihydrogen phosphate or bisulfate with easily operated equipment would be desired to allow economic manufacture.
One aspect of the present invention pertains to a process for making a quaternary ammonium dihydrogen phosphate or bisulfate salt comprising the steps of: (1) forming a first mixture by contacting a quaternary ammonium halide with: (a) a water-insoluble organic solvent capable of forming a ternary azeotrope with water and hydrogen halide and (b) an amount of water and sulfuric acid or phosphoric acid sufficient to maintain the temperature of the first mixture in the range of from about 98xc2x0 C. to about 105xc2x0 C. when heated; (2) heating the first mixture to a temperature sufficient to separate a ternary azeotrope comprised of hydrogen halide, water and the water-insoluble organic solvent from the first mixture to form a second mixture comprised of water, sulfuric acid or phosphoric acid, the water-insoluble organic solvent and a quaternary ammonium dihydrogen phosphate or bisulfate salt.
The quaternary ammonium dihydrogen phosphate or bisulfate salts can be used as phase transfer catalysts themselves or be readily converted to quaternary ammonium salts having anions not readily obtainable from the chloride salts such as the hydroxide, carbonate, nitrate, chromate, dichromate, vanadate, and tungstate salts. These salts are useful as phase transfer catalysts or as extractants for metals from aqueous solutions in hydrometallurgical metal recovery applications.
Another aspect of the present invention pertains to a liquid quaternary ammonium dihydrogen phosphate or bisulfate salt having a chloride impurity content of less than about one mole percent. Such liquids are practically insoluble in water and are completely soluble in an organic phase of a phase transfer reaction.
Still another aspect of the invention pertains to a process for making quaternary ammonium compounds wherein the anion, G, is other than bisulfate or dihydrogen phosphate wherein G is selected from the group consisting of hydroxide, carbonate, nitrate, chromate, dichromate, vanadate and tungstate.
Not applicable
One aspect of the present invention pertains to a process for making any quaternary ammonium bisulfate or dihydrogen phosphate salt of the general formula QHSO4 or QH2PO4 wherein Q is R1 R2 R3 R4N+ and wherein each of R1 R2 R3 R4 is independently an alkyl or cycloalkyl group having from 1 to 22 carbon atoms from any quaternary ammonium halide salt, QX, wherein Q is defined above and X is the anion of a distillable acid such as Fxe2x88x92, Clxe2x88x92, Brxe2x88x92 or Ixe2x88x92. The term distillable acid is defined as any Bronsted (hydrogen donating) acid which is capable of being vaporized and recondensed without degradation, either by itself or as an azeotrope. Examples include but are not limited to the hydrogen halides as well as most carboxylic acids.
The process according to the invention is based on the reaction of a quaternary ammonium halide in general or a quaternary ammonium chloride in particular with either sulfuric acid or phosphoric acid to produce a quaternary ammonium bisulfate or a quaternary ammonium dihydrogen phosphate and a hydrogen halide. While not wishing to be bound by theory, it is believed that the reaction is thermodynamically unfavored, but can be displaced by removal of the hydrogen halide via distillation of the hydrogen halide azeotrope with water and any solvent that forms a ternary azeotrope with a hydrogen halide and water such as benzene, toluene, heptane or octane when the excess sulfuric acid or phosphoric acid concentration is elevated and the water level in the mixture is low. There appears to be a relationship between the two; higher excess sulfuric acid allows more water to be present in the reaction and still gives good rates of hydrogen halide removal. Since the distillation removes water from the reaction, the desired level of water must be maintained by continuous or periodic addition of fresh water. When operating at atmospheric pressure, the amount of water is any amount of water and sulfuric acid sufficient to maintain the temperature of the reaction mixture in the range of from about 98xc2x0 C. to about 105xc2x0 C., preferably from about 102xc2x0 C. to about 103xc2x0 C. Alternatively, the reaction could be run by injecting steam into a mixture of the ammonium compound, organic solvent and sulfuric acid with a level of water present.
Any water-insoluble organic solvent capable of forming a ternary azeotrope with water and a hydrogen halide can be used. Toluene is a preferred solvent because it boils high enough to form an azeotrope with a substantial level of hydrogen halide, particularly HCl, but not so high that degradation of the product becomes excessive. Other such solvents that can be used include, but are not limited to, benzene, heptane and octane. While the process according to the invention can be carried out at any pressure, atmospheric pressure is preferred because of the corrosive nature of the distillate.
The process according to the invention can be used for making any quaternary ammonium compound of the formula QHSO4or QH2PO4 wherein Q is R1 R2 R3 R4N+ and wherein each of R1 R2 R3 R4 is independently an alkyl, or group having from 1 to about 22 carbon atoms from any quaternary ammonium halide salt.
The process according to the invention is particularly applicable to the preparation of methyl tri-alkylammonium salts but can be employed to make other quaternary ammonium compounds such as tetrabutyl and methyl tributyl ammonium salts.
The process according to the invention removes an equivalent amount of chloride but with the following advantages over known methods such as those of the comparative examples: less time-consuming; less labor intensive; requires smaller amounts of reagents to drive the exchange thereby resulting in cost and effluent disposal savings.
Another aspect of the present invention is a process according to the invention is a process for making quaternary ammonium salts of the formula
QG
wherein Q is defined as above and G is selected from the group consisting of hydroxide, carbonate, nitrate, chromate, dichromate, vanadate and tungstate. The process is comprised of the steps of (1) forming a first mixture by contacting a quaternary ammonium halide with: (a) a water-insoluble organic solvent capable of forming a ternary azeotrope with water and hydrogen halide and (b) an amount of water and sulfuric acid or phosphoric acid sufficient to maintain the temperature of the first mixture in the range of from about 98xc2x0 C. to about 105xc2x0 C. when heated; (2) heating the first mixture to a temperature sufficient to separate a ternary azeotrope comprised of hydrogen halide, water and the water-insoluble organic solvent from the first mixture to form a second mixture comprised of water, sulfuric acid or phosphoric acid, the water-insoluble organic solvent and a quaternary ammonium dihydrogen phosphate or bisulfate salt; (3) reacting the quaternary ammonium dihydrogen phosphate or bisulfate salt with an aqueous solution of a salt of anion G.
The following examples are meant to illustrate but not to limit the invention.